The present invention relates generally to automotive engines and, more particularly, is directed to a method and device for accurately positioning and aligning a guide sleeve into a bore of a cylinder head.
In conventional automotive engines, the intake and exhaust of gases into the respective cylinder chambers are controlled by valves. Specifically, each valve includes a valve head and a valve stem, with the valve stem slidable within a bore in the cylinder head and the valve head engagable with a valve seat at the entrance of the bore for opening and closing the intake and exhaust ports for the cylinder chamber. In such a case, a guide sleeve is conventionally inserted with a friction fit, into each bore so as to guide movement of the valve stem therein.
Conventionally, in order to insert a guide sleeve into a bore, the cylinder head is heated in an oven or by a torch and simultaneously, the guide sleeve is immersed into a solution of alcohol and dry ice to cool and thereby shrink the sleeve. The cooled guide sleeve is then forcibly inserted into the bore of the heated cylinder head by a press, a hammer, or other conventional means.
However, using such a method, it is impossible to accurately control alignment of the guide sleeve within the cylinder head. Thus, the guide sleeve is often not correctly aligned in the bore. Specifically, the axis of the guide sleeve will often be offset and/or inclined with respect to the axis of the bore in the cylinder head. The valve stem which slides within the guide sleeve will also be out of alignment with the bore in the cylinder head. This poor alignment of the valves will translate into deviations of 0.020 inch to 0.080 inch at the edge of a two inch diameter valve.
Because of such misalignment, the valve head will not accurately seat on the valve seat so that the suction and discharge ports for the cylinder chamber will not be completely closed at the respective times. It is therefore necessary to remove material from the valve seat in order to accurately position the valve head thereon. This removal operation is not only time consuming but also requires use of expensive equipment. For example, a carbide cutter with a pilot positioned by a new guide sleeve is used to remove the bulk of material. The next step requires the use of a rotary grinder to remove chatter marks caused by the carbide cutters. In the final step, the valve seat is lapped to achieve a perfect fit.
As a result of such time consuming operations, the time required to install, for example, 12 new valve guide sleeves according to the prior art, is approximately 3 to 4 hours, depending upon the degree of misalignment of each of the guide sleeves.